The present invention generally relates to integrated circuit (IC) packaging. More particularly, this invention relates to an IC power package and packaging method for a generator rectifier bridge, in which the package employs a metal-oxide-semiconductor field effect transistor (MOSFET).
Diodes are conventionally used in rectifier bridges for ac generators used in automotive applications. The diodes are often formed as press-fit packages with two connections that enable the packages to be readily installed in the rectifier bridge. One connection is made with a conductive base connected to one terminal of the diode, while the second connection is made with a pin connected to the opposite terminal of the diode. The package is installed by pressing the base into a bridge bracket, and then brazing the pin to the bridge circuit.
Automotive generators equipped with conventional diode-based rectifier bridges can be challenged as the number and power requirements of automobile accessories and systems increase, particularly as a result of low generator output at idle conditions. In certain applications, a larger generator or a battery with a higher rated output must be used, incurring both a size and weight penalty for the automobile. From a system standpoint, it would be advantageous to replace all of the rectifier diodes of an automotive ac generator with field effect transistors (FET) to allow for more precise control of the generator DC output. AC-DC conversion through FETs would allow phase shifting and power factor control, enabling higher charging system efficiency especially at low engine rpms. Such a capability would be especially desirable for automobiles equipped with a large number of power-hungry systems. However, FETs require three connectionsxe2x80x94one each for the source, drain and gate. Accordingly, the replacement of a diode-based rectifier bridge package with an FET-based package would appear to require a redesigned rectifier bridge and potentially additional system modifications, all of which are undesirable from a system and assembly standpoint.
The present invention provides an IC power package particularly suitable for use as a rectifier for an automotive ac generator, as well as an IC packaging method. The power package comprises an electrically-conductive base, a MOSFET die mounted to the base so that the drain region of the MOSFET is electrically connected to the base, an electrically-conductive pin mounted to the die and electrically connected to the source region of the MOSFET, and an electrically-conductive member electrically connected to the gate region of the MOSFET. The conductive member can take several forms, including a second pin or a leadframe mounted to the die, or an annular-shaped member mounted to the base by an electrically-insulative member. In the latter embodiment, the annular-shaped member may be electrically connected to the gate region with a bond wire. The die is preferably encapsulated on the base, yielding a rugged IC package with three connections provided by the base, pin and conductive member.
In view of the above, it can be appreciated that the base and pin of the IC package of this invention can be substantially similar to that of a conventional diode-based rectifier package. Therefore, the IC package of this invention is compatible with existing generator rectifier bridge designs, so that only minimal modifications are required to use the package with conventional generator designs. The packaging method of this invention is also uncomplicated, and amenable to fixturing and conventional processing to yield a package whose base, pin and conductive member are precisely aligned for installation.
With the IC package of this invention, more precise control of an ac generator output can be achieved than with conventional diode-based rectifier bridges. Also possible are phase shifting and power factor control, enabling higher charging system efficiency especially at low engine rpms. The IC package of this invention achieves these advantages without requiring a redesigned rectifier bridge or other significant system modifications, even though the package has one more connection than that required for a diode-based rectifier bridge. Finally, while particularly suitable for use with ac generators, the present invention and its advantages should find use in a variety of applications, including high wattage audio/video equipment, electric motor controllers, etc.
Other objects and advantages of this invention will be better appreciated from the following detailed description.